It is known to use fluorescent quenching to indicate the presence of certain species of interest. A fluorescent material emits a specific wavelength and intensity of light which has a specific emission lifetime, upon excitation by a specific wavelength which is lower than the emitted wavelength. The intensity and lifetime of the emission is dependent upon the concentration of oxygen in contact with the fluorescent material. As the oxygen concentration increases the fluorescent emission intensity and lifetime decreases and the increase and decrease are directly proportional to one another.
Sensors used inside fuel tanks consist of a fluorescent material surface which is exposed to the fuel tank environment. A reduction in the fluorescent material's emission intensity and lifetime in the presence of oxygen gives a direct measure of oxygen concentration around the sensor surface. The fluorescent emission of a material that is electromagnetically excited decreases in direct proportion to the concentration of a species of interest. Materials such as platinum tetrakis pentafluorophenyl porphyrin and platinum octaethylporphyrin are used as gaseous oxygen sensing materials. However, the fuel tank environment is harsh and can cause the fluorescent material to degrade. This degradation of the material will result in a reduction in the intensity and changes in lifetime of fluorescent emission and this can be incorrectly interpreted as a higher oxygen level.